A joint structure for joining an insertion shaft and a reception side shaft may be realized by damping force adjusting means provided in a shock absorber of a suspension device such as a front fork or a rear cushion unit, for example.
JP08-183488A discloses damping force adjusting means for a rear cushion unit that suspends a rear wheel of a motorcycle in order to damp road surface vibration input into the rear wheel.
The rear cushion unit disclosed in JP08-183488A is constituted by a suspension spring that absorbs the road surface vibration and a damper device that damps an expansion/contraction motion of the rear cushion unit accompanying absorption of the road surface vibration.
The damper device includes a cylinder housing a working fluid, a rod that advances and retreats through the cylinder, a piston that is held on the rod so as to delimit an interior of the cylinder into an expansion side chamber and a contraction side chamber, and a reservoir tank that is provided on an exterior of the cylinder so as to communicate with the contraction side chamber and compensates for variation in an internal volume of the cylinder occurring as the rod advances and retreats through the cylinder.
A connecting passage that connects the contraction side chamber to the reservoir tank is closed by a base member. The base member includes an expansion side port and a contraction side port that connect the contraction side chamber to the reservoir tank. An expansion side check valve that allows the working fluid to flow only from the reservoir tank into the contraction side chamber is provided in the expansion side port. A contraction side damping force generating valve that allows the working fluid to flow only from the contraction side chamber into the reservoir tank and generates a predetermined damping force at that time is provided in the contraction side port. The damper device also includes damping force adjusting means for adjusting the damping force. The damping force adjusting means includes a bypass passage that connects the contraction side chamber to the reservoir tank without passing through the contraction side damping force generating valve, a needle valve that modifies an opening amount of the bypass passage, and an adjuster that drives the needle valve.
The opening amount of the bypass passage is modified by operating the adjuster to rotate such that a pointed end portion of the needle valve advances and retreats through the bypass passage. Accordingly, a flow rate of the working fluid passing through the contraction side damping force generating valve is modified, and as a result, the damping force is adjusted.
In JP08-183488A, a joint structure is used to join the needle valve to the adjuster. The joint structure is constituted by a projection formed on one end of the adjuster and having a pair of opposing planar portions, and a latch hole formed in a back surface of the needle valve, into which the projection formed on the adjuster is inserted to be capable of advancing and retreating. The needle valve is disposed in and screwed to a tubular needle sliding hole, and during the rotary operation of the adjuster, the needle valve rotates so as to move through the needle sliding hole in an axial direction.